Electric power transmission is a process in the delivery of electricity to consumers. In general, the term “electric power transmission” refers to the bulk transfer of electrical power from place to place, for example, between a power plant and a substation near a populated area. Due to the large amount of power involved, electric transmission normally takes place at high voltage (100 kV or above). Transformers are used at the substations to step the voltage down to a lower voltage for distribution to commercial and residential users. Other power transfer equipment utilized by the electrical utility industry includes, but is not limited to tap changers, circuit breakers, switches, capacitors, reactors, and the like.
Electric power transfer equipment is frequently filled with a fluid, typically of a mineral oil origin, that generally serves as a dielectric media, an insulator, and a heat transfer agent. During normal use this fluid undergoes a slow degradation to yield gases that collect in the oil. When there is an electrical fault within the transformer, these gases are generated more rapidly. Each of a number of fault conditions possible within a transformer generates certain key gases and a distribution pattern of these gases. Thus, the character of the fault condition giving rise to the gases may be ascertained by determining the various gases present in the transformer fluid and their amounts.
Dissolved gas analysis (DGA) is a widely used predictive maintenance technique for monitoring the collection and rate of generation of theses gases in liquid-filled electric power transfer equipment, in order to gauge the operation of such equipment. On-line dissolved gas analysis systems can provide analysis of multiple gases, for example, hydrogen (H2), oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). Samples may be taken periodically, for example, every four hours, from each transformer being monitored. This sample rate desirably increases to, for example, hourly if predefined thresholds for an individual gas, or if a rate of change for an individual gas, is reached. At a utility managing many transformers, this sample rate yields a plethora of data samples, each of which is to be analyzed.
Conventional online dissolved gas analysis systems are based on directly comparing measured quantities to threshold values (constants) and threshold (constants) gas generation rates. While this allows power producers and distributors to ascertain when certain measured quantities fall outside the threshold values, this approach generates false alarms of equipment malfunction. Existing dissolved gas analysis techniques cannot distinguish gas generation rates caused by faults and incipient faults from acceptable gas generation rates caused by periodic loading of the liquid-filled electric power transfer equipment.